1. Field of the Invention
The present invention relates generally to communications networking, and more specifically, to trafficking packets in a communications network.
2. Related Art
Architects of communications networks continuously seek to achieve an optimal balance among various network characteristics. Such characteristics include bandwidth demand and quality of service parameters, such as latency, loss, or priority. For example, data-over-cable networks are expanding the variety of services traditionally provided to subscribers. In addition to television broadcasts, cable providers are offering telephony, messaging, and Internet services. As a result, additional bandwidth is needed to support the timely delivery of these services.
Moreover, traditional cable broadcasts primarily require one-way communications from a cable service provider to a subscriber's home. As interactive or personal television services and other nontraditional cable services continue to be offered, communications media used to support one-way communications must now contend with an increased demand for bi-directional communications.
In a conventional cable television communications network, a communications device (such as a cable modem) requests bandwidth from a headend device prior to transmitting data to its destination. The headend device allocates bandwidth to the communications device based on availability and the competing demands from other communications devices. Typically, bandwidth is available to transmit signals downstream to the communications device. However in the upstream, bandwidth is more limited and must be arbitrated among the competing communications devices.
Depending on the type of service being hosted by the communications device, some communication devices or their services are granted higher priority over others. For example, telephony is less tolerant of latency, jitter, and loss than a data messaging service. Although some degree of latency and loss may be tolerated by data services, such latency and loss can be problematic to voice scheduling. Therefore, methods are needed to permit high priority services to operate with minimum latency.
During voice communications, calls come and go independently of each other. In addition, if activity detection is used, silence and active periods during different calls also occur independently. Hence, the number of voice calls active in a given time period can frequently change. This means that grant size varies accordingly. These dynamics translate to the transmission time of a given call may be at the beginning of a grant in some periods and at the end of the grant in others. Hence, a call can suffer a jitter delay of up to the maximum grant size. This jitter delay, also called concatenation jitter, can be limited to a given value by limiting the number of voice calls that are concatenated in the same grant transmission. If more calls need to be supported, the calls can be grouped in separate grants assigned to the same, for example, cable modem. In this case, system efficiency is compromised for a better jitter bound (i.e., less variability in grant arrival).
Therefore, a method is needed to address the above problems.